1. Field of the Invention
The present invention generally relates to an endoscope, and more particularly to an imaging unit used in an endoscope capable of providing focusing and/or zooming functions.
2. Description of the Related Art
There have been widely used various endoscopes for medical and other purposes to visualize the interior of a cavity, such as a hollow organ. One typical endoscope comprises a handpiece including a manipulating member mounted thereon, a tip unit including a generally cylindrical housing having front and rear ends, and an insertion tube extending between and interconnecting the handpiece and the tip unit, the insertion tube having a proximal end connected to the handpiece and a distal end connected to the rear end of the housing of the tip unit. When such endoscope is used for medical purposes, the tip unit and a part of the insertion tube are inserted into a human body. An imaging unit is housed in the housing of the tip unit for forming an image as viewed in a view field in front of the tip unit. A manipulation cable assembly is received in the insertion tube. The manipulation cable assembly has a proximal end operatively connected to the manipulating member on the handpiece and a distal end operatively connected to the imaging unit so as to allow a user to manipulate the imaging unit through the manipulating member on the handpiece. The imaging unit comprises a plurality of optical elements forming an optical system and a support and guide mechanism for supporting and/or guiding the plurality of optical elements.
One exemplified endoscope having the above construction is disclosed in Japanese published patent application No. Sho-63-269113 published on Nov. 7, 1998. According to this patent application, some of the lenses of the imaging unit are fixedly supported on the housing of the tip unit while the others are movable relative to the housing. The support and guide mechanism of the imaging unit comprises a movable carriage carrying the movable lenses thereon. The movable carriage is supported and guided for axial movement relative to the housing. The distal end of the manipulation cable assembly is operatively connected to the movable carriage. The movable carriage is driven through the manipulation cable assembly for axial movement relative to the housing in order to achieve focusing operation of the imaging unit.
Another tip unit of an endoscope having a similar imaging unit is disclosed in Japanese patent publication No. Hei-5-12686 published on Feb. 18, 1993. According to this patent publication, a movable carriage is driven through a manipulation cable assembly in order to achieve zooming operation of the imaging unit.
In either case, the pull and/or push forces required for driving the movable carriage will directly act on the movable carriage from the manipulation cable, while the movable carriage is supported and guided for axial movement by a certain support and guide mechanism which can not help suffering from allowances and clearances inevitably existing between movable components for smooth operation of the imaging unit. Such allowances and clearances often cause a minute but harmful tilt of the movable carriage, leading to partial blurring of the resultant image observed.